"Looking past the Metro hype, the Build conference also revealed promising road maps for C#, Visual Studio, and the .Net platform as a whole. Perhaps the most exciting demo of the conference for .Net developers, however, was Project Roslyn, a new technology that Microsoft made available yesterday as a Community Technology Preview. Roslyn aims to bring powerful new features to C#, Visual Basic, and Visual Studio, but it's really much more than that. If it succeeds, it will reinvent how we view compilers and compiled languages altogether."

How is exposing the internal API publicly a major departure and reinvention of compilers?

Compilers are tansformed from this classic vision of take a source file in -> generate code.

Now, every aspect of the compiler is a service. I can do metaprogramming by transforming syntax if thats what I need. I can gather data from a previously or newly compiled program (or myself) using semantics.

I can transform code at the semantic level for an even more targeted approach to metaprogramming.

I can query the Solution/Project API and perform the same syntax/semantic analysis on those documents, or whatever else I want, then save the project.

I'm not saying it's not great that they are exposing API that will stay stable. I just don't get the hype over this.
Please do hype up anything that grows up from this to be ridiculously fun or novel. But as it stands, Roslyn is not revolutionary or anything like that.

I suppose that's your opinion, I just strongly disagree.

I view this in the same light I view other exciting framework developments. When LINQ launched people were asking how this would be revolutionary, the same with Rx. Some concepts just take time to grasp.